This invention pertains to high temperature fuel cells and, in particular, to electrode-electrolyte assemblies for use in such cells.
Higher temperature fuel cells such as, for example, molten carbonate cells, have the capability of producing electric power from coal at system efficiencies approaching 50 percent. These cells are thus an attractive candidate for alternative power sources which conserve energy.
In the development of high temperature fuel cells to date, it is customary to form the high temperature cells from discrete cathode and anode electrodes which sandwich a discrete electrolyte tile. The electrolyte-electrode assembly is then itself sandwiched between cathode and anode gas housings to complete the cell. It is also customary in this type of cell to add to the electrolyte tile a binder or filler material to provide a mechanism for preventing gas cross-over.
With the electrolyte-electrode assembly constructed in the above manner, it is found that the fuel cell exhibits a certain degree of contact resistance due to the lack of good contact over substantially the entire areas of the stacked components. IR losses also occur due to the necessary thickness of the electrolyte tile. Limited fuel cell bubble pressure is also evidenced, owing to the limited amounts of filler which can be added to the tile. Finally, there is a tendency of the tile to crack during thermal cycling. This cracking allows mixing of anode and cathode gases (gas cross-over) which results in cell failure.
While the aforesaid cracking of the electrolyte tile is not fully understood, it is generally believed to be due, at least in part, to the rather different coefficients of thermal expansion of the tile and electrodes. These differences and their effects are further aggravated, by the discrete layer arrangement of the assembly.
It is an object of the present invention to provide an electrolyte electrode assembly for realizing an improved high temperature fuel cell.
It is a further object of the present invention to provide an electrolyte-electrode assembly for realizing a high temperature fuel cell with increased power output and efficiency.
It is yet a further object of the present invention to provide an electrode-electrolyte assembly with increased resistance to cracking under thermal cycling.
It is also an object of the present invention to provide an electrolyte-electrode assembly having increased bubble pressure and reduced IR losses.